The Collaborative International Dictionary of English v.0.48:

Balloon \Bal*loon"\, v. t.
   To take up in, or as if in, a balloon.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Balloon \Bal*loon"\, v. i.
   1. To go up or voyage in a balloon.
      [1913 Webster]

   2. To expand, or puff out, like a balloon.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Balloon \Bal*loon"\, n. [F. ballon, aug. of balle ball: cf. It.
   ballone. See 1st Ball, n., and cf. Pallone.]
   1. A bag made of silk or other light material, and filled
      with hydrogen gas or heated air, so as to rise and float
      in the atmosphere; especially, one with a car attached for
      a["e]rial navigation.
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   2. (Arch.) A ball or globe on the top of a pillar, church,
      etc., as at St. Paul's, in London. [R.]
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   3. (Chem.) A round vessel, usually with a short neck, to hold
      or receive whatever is distilled; a glass vessel of a
      spherical form.
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   4. (Pyrotechnics) A bomb or shell. [Obs.]
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   5. A game played with a large inflated ball. [Obs.]
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   6. (Engraving) The outline inclosing words represented as
      coming from the mouth of a pictured figure.
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   Air balloon, a balloon for a["e]rial navigation.

   Balloon frame (Carp.), a house frame constructed altogether
      of small timber.

   Balloon net, a variety of woven lace in which the weft
      threads are twisted in a peculiar manner around the warp.
      [1913 Webster]

WordNet (r) 3.0 (2006):

balloon
    n 1: large tough nonrigid bag filled with gas or heated air
    2: small thin inflatable rubber bag with narrow neck
    v 1: ride in a hot-air balloon; "He tried to balloon around the
         earth but storms forced him to land in China"
    2: become inflated; "The sails ballooned" [syn: balloon,
       inflate, billow]